Nuclear simple sequence repeats (nSSRs), together with 16 different enzyme loci, were used to analyzegenetic diversity and differentiation among beech (Fagus orientalis Lipsky) populations along two altitudinalgradients in Hyrcanian forests of Iran. Both enzymes and nSSR analyses revealed a high level ofgenetic diversity in natural populations of F. orientalis. The genetic diversity, estimated by expected heterozygosity, was 0.19 (by enzymes) and 0.65 (by nSSRs). Genetic variation across both markers did not reveal genetic structuring along altitudinal transects. There was less genetic variation among altitudinal gradients within transects compared to transect sites. Differentiation assays and analysis of molecular variance(AMOVA) indicated that there was a relatively low genetic differentiation among populations, and just 1%and 5% of the genetic variation occurred among populations by nSSR and enzyme data, respectively.Mantel tests showed that there was not a significant correlation between the genetic distances among populations and the distance of elevation. The results of the present study indicate that the relatively low genetic differentiation among F. orientalis populations at different elevations was not caused by ecological factors. These patterns suggest that higher rates of gene flow along altitudinal gradients within transects, thanbetween transects; a process that could question altitudinal adaptation.